var Ball={
	div:document.getElementById('ball'),
	left:subs(window.getComputedStyle(document.getElementById('ball')).left),
	top:subs(window.getComputedStyle(document.getElementById('ball')).top),
	radio:10,//半径
	xa:5,//横向速度
	ya:-5,//纵向速度
	init:function(){
		this.left=subs(window.getComputedStyle(this.div).left);
		this.top=subs(window.getComputedStyle(this.div).top);
	},
	move:function(){
		if(this.left>360-this.radio || this.left<this.radio){
			//超出左右边界
			this.xa*=-1;
		}
		if(this.top<=0){
		//超出下边界
			this.ya*=-1;
		}
		this.div.style.left=this.left+this.xa+'px';
		this.div.style.top=this.top+this.ya+'px';
		this.init();
	}
}
